Competition Flashcards
Competition is only found
between species of overlapping niches
Degree of niche overlap impacts degree of
competition
Complete Competitors
Share the same niche. Limited by the same one resource
Competitive Exclusion Principle
Complete competitors cannot coexist indefinitely
Liebig’s law of the minimum
population increases until the supply of the most limiting resource prevents it from increasing further.
True or false. All competitors cannot coexist.
False. Complete competitors cannot co exist because theyre limited by the same resources. Competitors can if they arent limited by resources.
We need to extend the … model to consider the impact of each species on the other
logistic
Lotka Voltera Competition Model
Species 1: dN/dt =r1n1(1-N1+aN2/K1)
Species 2: dN/dt=r2n2(1-N2+BN2/K2)
a in the Lotka Voltera Competition Model
Competitive effect of species 2 on species 1.
-Species 1/Species 2
B in the Lotka Voltera Competition Model
Competitive effect of species 1 on species 2
-Species 2/Species 1
Two Species Equilibrium
When the observed growth of both species is 0
When species 1 is at equilibrium, the equation is
N1=K1-aN2
When N1 =0 then
Either:
N2=K1/a
or
N2=K2
When N2=0 then
N1=K1
or
N1=K2/B
Species 1 is on … and has … vectors
x axis, horizontal
Species 2 is on … and has … vectors
y axis, vertical
Phase Plane Diagram
Put species 1 and species 2 on one graph. Four possible outcomes
If isocline for species 1 is farther out …
species 2 will go extinct
Is isocline for species 2 is farther out…
species 1 will go extinct
There is an unstable equilibrium (two possible final equilibrium points) when
K1 and K2 are the outer most parts. B and a are both high.
There is a stable equilibrium (coexistence) when
K1 and K2 are the inner most parts.
Coexistence can occur when intraspecific competition is
stronger than interspecific competiton. (B and a <1)
Two types of true competition
Exploitation and Interference Competition
Exploitation Competition
Individuals most efficiently consume the resource. This can drive down resource abundance so that others can persist.
Interference Competition
One species actively prevents the other, by behavioral or chemical interference, from exploiting the resource.
Allelo-chemicals/Allelopathy
Secondary compounds produced by some plant species that kill neighbors.
Apparent competition
Impacts resembling competition but not due to shared resources. Mediated by a shared predator or parasite. Ex. Indirect negative impact of pheasants on partridges via nematodes.
The starting point in lotka voleta is
pop of species 1, pop of species 2
Cyclic oscillations
Regular oscillations over a period of time. Fluctuations can occur synchronously among populations and species
Delays related to … are common in nature
gestation
Delayed Density Dependence
When dependence occurs based on density some point in the past.
Degree of cycling in populations depends on r*…
t. Time delay.
Larger t (time delay) means
bigger overshoot of K later on
When rt is smaller than 0.37…
the population approaches K without oscillations
When rt is in the middle of 0.37 and 1.57
There are damped oscillations. Amplitude declines over time.
When rt is greater than 1.57
Oscillations. Big time delay
Delayed density dependence can also be caused by (other than gestation)
energy/nutrient storage
Peak density is reach once every … years
r*t
Smaller populations … quicker but also … quicker
grow, go extinct
Deterministic model
Used fixed values (ignoring random variation)
Stochastic model
Incorporate random variation in population growth rates
Demographic Stochasticity
Births and deaths happen in integers. Random differences among individuals cause population rates to vary from the expected mean. Impact important for small populations
Environmental Stochasticity
Variation in birth & death rates due to random environmental changes.
Impact of environmental and demographic stochasticity more important for … populations
smaller
